DNA

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DNA is the molecule that carries all our inherited information. It has a double-helix structure, which contains chains of nucleotide bases joined together in pairs. Each individual has its own unique genetic message. This genetic code determines which amino acids are joined together to form proteins. There are only 20 naturally forming amino acids, but joined together they can make an almost infinite number of proteins. They are joined together on the surface of a ribosome. A sequence of 3 base pairs on the DNA  is transcribed to give the corresponding base pairs of mRNA in the nucleus as part of the process of protein synthesis. A 3-base sequence of DNA or RNA is known as a codon. Some codons code for an amino acids whist others code for te start or end of a particular sequence. However the genetic code is also non-overlapping and degenerate.

Protein Synthesis.

Transcription.

The DNA that carries the genetic message is in the nucleus, but proteins are made on the ribosomes. The message of the DNA has to be transcribed to form mRNA. The breakdown of hydrogen bonds between the bases in the double helix is catalysed by enzymes called DNA-directed RNA polymerase. Only the 5' prime DNA strand is transcribed to give a single strand of mRNA. This DNA strand is called the template strand. RNA polymerase joins many small nucleotide units together to form mRNA. Every triplet code of the DNA gives rise to a complementary codon on the mRNA. The mRNA strand only has 1 difference, T is replaced with U.  The mRNA molecules pass easily through pores in the nuclear membranes, carrying the genetic message to the cytoplasm.

Translation.

tRNA picks up specific amino acids and carries them to the surface…

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